Video Data Decoding And Decoding Method

ABSTRACT

A video data decoding device and method. The device has an entropy decoder, and a WPP status control module for selecting an operating status according to a syntax structure of a coding tree unit. The device further has a memory selector for controlling the operating status of a memory. The memory has one buffer memory and two update memories. When the number of columns of a row of coding tree units currently decoded is larger than three, the context data of the coding tree units currently decoded is written into the buffer memory and one of the update memories; and when it is determined that the context data of the coding tree units referred by a first coding tree unit in a next row of coding tree units is available when the next row of coding tree units starts to be parsed, the data in the buffer memory is replicated.

TECHNICAL FIELD

The present invention relates to the technical field of video datacoding and decoding, and particularly, to a video data decoding deviceand a decoding method implemented by using the video data decodingdevice. The present invention is based on Chinese Patent Application No.201510485813.9 filed on Aug. 10, 2015, the contents of which areincorporated herein by reference closely related to the presentinvention.

BACKGROUND ART

With the development of video coding and decoding techniques, people notonly require a higher definition of video images but also have a highrequirement on the coding and decoding speeds of the video images.Although the current predominant video coding and decoding protocols canmeet the requirements for occasions such as high definition television,video monitoring and video conferencing, it will become increasinglydifficult for the original video protocols to meet these requirements ofhigh compression, a high code rate, high fidelity and the like for ultrahigh-definition video such as 4K×2K and 8K×4K with the continuousdevelopment of the video playing industry and the continuous improvementof the user experience. The video compression protocol standard HEVC(the H.265 protocol), as a new generation of video coding and decodingprotocol, has the image compression ratio increased by about 50% ascompared to the previous generation of the H.264 protocol under thepremise of the image quality, and has the image structure greatlychanged to enlarge the block size and incorporate parallel processing soas to well meet the requirements for processing the ultrahigh-definition video images.

In the H.265 protocol, the video is divided into a plurality of slices,each of which generally comprises a plurality of coding tree units(CTUs). Video decoding is to parse each of the coding tree units toobtain image data to be outputted. The concept of wavefront parallelprocessing (WPP) is proposed in the H.265 protocol, and this method ismainly for parallel processing of the coding tree units in the videoslices to increase the image coding and decoding speeds and the imagecompression ratio.

For one video slice having a plurality of rows and a plurality ofcolumns in the WPP mode, decoding of coding tree units in a next codingtree unit row is started once decoding of two coding tree units in acurrent coding tree unit row is completed, and so forth. Thus, decodingof the coding tree units of the next row is gradually started so as toachieve parallel coding and decoding processing of the images. Forexample, as shown in FIG. 1, when a coding tree unit CTU16 in a firstrow is being decoded, decoding of a coding tree unit CTU24 in a secondrow, a coding tree unit CTU32 in a third row and a first coding treeunit CTU40 in a fourth row should be started.

The H.265 protocol adopts an arithmetic coding method namedContext-based Adaptive Binary Arithmetic Coding (CABAC). During CABACdecoding in the WPP mode, image decoding of each row should be startedby obtaining corresponding data such as context variables according toavailability of a second coding tree unit in the previous row (exceptthe video slice which has only one coding tree unit in a row) and thefact whether a starting position of the video slice is encountered,i.e., should be reinitialized or directly replicated so that arithmeticdecoding contained in the video decoding process can proceed correctly.

The existing video decoding chip generally comprises an embodiedprogram, which includes an entropy decoding unit for carrying outentropy decoding on the video. As shown in FIG. 2, the entropy decodingunit comprises a syntax element status control module 11, a contextvariable index calculation module 12, an arithmetic decoding module 13and an inverse binarization module 14. The syntax element status controlmodule 11 gives a syntax element parsing status and transitionindication by receiving an external control signal and information fedback from the context variable index calculation module 12, thearithmetic decoding module 13 and the inverse binarization module 14 andcarrying out related operations. Under control of the syntax elementparsing status control module 11, the context variable index calculationmodule 12 completes initialization and update of context data and alsocompletes calculation of the syntax element context index in the entropydecoding process. The arithmetic decoding module 13 mainly completesparsing of an original code stream to a syntax element binary codestring and transmits the parsing result in the form of a binary value tothe inverse binarization module 14. The inverse binarization module 14receives the binary value given by the arithmetic decoding module 13 andimplements the binary to decimal parsing of the syntax element.

Technical Problem

As a large amount of context data is generated in the decoding process,these data is usually stored in a static random access memory (SRAM) andthe entropy decoding unit usually stores the context data into only onestatic random access memory. The static random access memory not onlyneeds to store the updated context data but also needs to replicate thecontext data as reference coding tree units so as to save the desiredcontext data for subsequent decoding. As data update and cache and datareplication have to be carried out in different address spaces when onestatic random access memory is used, it cannot be ensured that dataupdate and replication are executed simultaneously in the decodingprocess, and this affects the decoding speed of the video and leads toslow playing of the video images.

Technical Solutions

A primary objective of the present invention is to provide a videodecoding device for increasing the decoding speed of video images.Another objective of the present invention is to provide a videodecoding method for increasing the video decoding efficiency.

To achieve the aforesaid primary objective, the video decoding deviceprovided by the present invention comprises an entropy decoding unit.The entropy decoding unit comprises a syntax element status controlmodule for receiving an external signal and outputting syntax elementparsing status and transition information and a context variable indexcalculation module for receiving the information outputted by the syntaxelement status control module. The context variable index calculationmodule also initializes and updates context data, and calculates indexinformation of the context data. The entropy decoding unit furthercomprises an arithmetic decoding module for parsing original video codestream data into syntax element binary code string data and an inversebinarization module for converting the binary code string data outputtedby the arithmetic decoding module into decimal data. The video datadecoding device further comprises a WPP status control module forselecting an operating status according to a syntax structure of acoding tree unit currently decoded and a memory selection module forcontrolling the operating status of a memory according to informationoutputted by the WPP status control module. The memory at leastcomprises one buffer memory and two update memories. When the number ofcolumns of a row of coding tree units currently decoded is larger thanthree, the context data of the coding tree units currently decoded iswritten into the buffer memory and one of the update memories. When itis determined that the context data of the coding tree units referred bya first coding tree unit in a next row of coding tree units is availablewhen parsing of the next row of coding tree units starts to be parsed,the data in the buffer memory is replicated into the other of the updatememories.

In one preferred embodiment, the memory selection module is furtherconfigured to continue to use the original update memory for updatingthe context data of the coding tree units when it is determined that thecontext data of the coding tree units referred by a first coding treeunit in a next row of coding tree units is unavailable when the next rowof coding tree units starts to be parsed.

As can be seen from this, the original update memory continues to beused for updating the context data of the coding tree units when thereferred context data of the coding tree units is unavailable. This canavoid replication of the data and switching of the static random accessmemory, thus decreasing the power consumption of the video decodingdevice and increasing the use efficiency of the hardware.

In a further embodiment, the memory selection module is furtherconfigured to, while writing the context data of the coding tree unitscurrently decoded into the buffer memory and one of the update memories,write the context data into the other of the update memories.

As can be seen, the updated context data is written into three bufferssimultaneously in the initial video decoding period, and this can reducethe operation of data replication so as to increase the video decodingefficiency.

In a further embodiment, the memory selection module is furtherconfigured to use one of the update memories to store the context dataof the coding tree units currently decoded when the number of columns ofa row of coding tree units currently decoded is smaller than three. Ascan be seen from this, when the number of columns of a row of codingtree units currently decoded is smaller than three, the context datastored in the current update memory can be directly used for the nextrow of coding tree units. Therefore, there is no need for replication ofthe context data, and only one update memory is needed to store theupdated context data.

In a further embodiment, the WPP status control module records at leastthree operating statuses, and the memory selection module controlsswitching of the operating statuses of the buffer memory and the updatememories according to the information of the operating statusesoutputted by the WPP status control module.

As can be seen, the WPP status control module records a plurality ofdifferent operating statuses, and the buffer memory and the updatememories operate in the different operating statuses respectively. Theoperating statuses of the three memories can be controlled convenientlythrough switching of the plurality of operating statuses so as to meetthe requirement of rapid switching of the operating statuses of thememories and increase the video decoding speed.

To achieve the aforesaid another objective, the video decoding methodprovided by the present invention comprises an entropy decoding step:receiving an external signal and outputting syntax element parsingstatus and transition information, concurrently initializing andupdating context data of coding tree units to be decoded, calculatingindex information of the context data, parsing original video codestream data into syntax element binary code string data, and convertingthe binary code string data outputted by an arithmetic decoding moduleinto decimal data. The video decoding method further comprises a memoryselection step: in execution of the entropy decoding step, using atleast one buffer memory and two update memories to store the contextdata; when the number of columns of a row of coding tree units currentlydecoded is larger than three, writing the context data of the codingtree units currently decoded into the buffer memory and one of theupdate memories; and when it is determined that the context data of thecoding tree units referred by a first coding tree unit in a next row ofcoding tree units is available when the next row of coding tree unitsstarts to be parsed, replicating the data in the buffer memory into theother of the update memories.

Advantageous Effects

The video data decoding device provided by the present invention caneffectively increase the decoding efficiency to ensure fluency of videoplaying, and increases the video decoding efficiency by increasing theefficiency of writing data into the update memory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view of a coding tree unit in videodecoding.

FIG. 2 is a block diagram of the structure of an existing video decodingdevice.

FIG. 3 is a block diagram of the structure of an embodiment of a videodecoding device of the present invention.

FIG. 4 is a transition diagram of five statuses in an embodiment of avideo decoding method of the present invention.

FIG. 5 is a schematic view showing operating statuses of a buffer memoryand update memories in the embodiment of the video decoding method ofthe present invention.

Hereinbelow, the present invention will be further described inconjunction with the attached drawings and embodiments.

DETAILED DESCRIPTION OF THE INVENTION

The video decoding device of the present invention is configured for WPPCABAC decoding with the H.265 protocol in the serial manner, i.e., forvideo sequence decoding in the WPP mode in the serial manner. The videodecoding method of the present invention is an entropy decoding methodimplemented using the above video decoding device.

Referring to FIG. 3, the video decoding device of the present inventionhas an entropy decoding unit 20, and the entropy decoding unit 20 has asyntax element status control module 21, a context variable indexcalculation module 22, an arithmetic decoding module 23 and an inversebinarization module 24. The syntax element status control module 21gives a syntax element parsing status and transition indication byreceiving an external control signal and information fed back from thecontext variable index calculation module 22, the arithmetic decodingmodule 23 and the inverse binarization module 24 and carrying outoperations. Under control of the syntax element parsing status controlmodule 21, the context variable index calculation module 22 completesinitialization and update of context data and also completes calculationof the syntax element context index in the entropy decoding process. Thearithmetic decoding module 23 mainly completes parsing of an originalcode stream to a syntax element binary code string and transmits theparsing result in the form of a binary value to the inverse binarizationmodule 24. The inverse binarization module 24 receives the binary valuegiven by the arithmetic decoding module 23 and implements the binary todecimal parsing of the syntax element.

The video decoding device further comprises a WPP status control module27 and a memory selection module 28. The WPP status control module 27 isconfigured to select an operating status of the video decoding device,and specifically, control the operating statuses of three memories. Inthis embodiment, the video decoding device uses three static randomaccess memories for storing the context data generated in the videodecoding process, where one of the memories is a buffer memory labelledas M1 and two of the memories are update memories labelled as M0 and M2respectively. Of course, the static random access memories may also bereplaced by other types of memories such as dynamic random accessmemories (DRAMs). The three memories implement different functions indifferent operating statuses respectively such as receiving the updatedcontext data and replicating the stored data. Hereinbelow, the operatingprocess of the three memories in three operating statuses will bedescribed in detail.

The memory selection module 28 receives the information outputted by theWPP status control module 27, which is information about selection ofthe operating statuses. The memory selection module 28 selects thememories for initialization of the context data, update of the contextdata and replication of the context data according to the informationoutputted by the WPP status control module 27, and concurrentlytransmits corresponding memory control signals to modules of the entropydecoding unit 20 so as to achieve timely interaction of the contextdata.

According to the requirement of entropy decoding with the H.265protocol, decoding in the WPP mode is activated only when the number ofcolumns of a row of coding tree units currently decoded is larger thantwo, and conventional entropy decoding is used when the number ofcolumns of the coding tree units is one or two. Therefore, in thisembodiment, five statuses (i.e., a dummy status, three operatingstatuses and an end status) are formed according to the operatingstatuses of the three memories in the decoding process, where the threeoperating statuses are status S0, status S1 and status S2 respectively.In different statuses, the three memories can complete operations suchas initialization, update of the context data and replication of thecontext data. Hereinbelow, operations in the five statuses will beintroduced.

In the dummy status, none of the three memories execute any operation.In the operating status S0, decoding of current coding tree units isstarted, and the three memories M0, M1 and M2 are initializedconcurrently. The context data generated in the decoding process isstored all along in the update memory M0, while the buffer memory M1 andthe update memory M2 only have the context data of two coding tree unitsstored therein.

In the operating status S1, the context data generated in the decodingprocess is stored all along in the update memory M2. Meanwhile, thebuffer memory M1 has the context data of a first coding tree unit and asecond coding tree unit stored therein, and when a third coding treeunit is decoding, the context data stored in the buffer memory M1 isreplicated into the update memory M0.

In the operating status S2, the context data generated in the decodingprocess is stored all along in the update memory M0. Meanwhile, thebuffer memory M1 has the context data of the first coding tree unit andthe second coding tree unit stored therein, and when the third codingtree unit is decoding, the context data stored in the buffer memory M1is replicated into the update memory M2.

The WPP status control module 27 outputs decoding end status informationin the end status, and then transitions to the dummy status.

Hereinbelow, transition among the above five statuses will be describedwith reference to FIG. 4.

In the dummy status, if the current image decoding process is in the WPPcoding mode, then decoding of a first slice is activated. Moreover, whenthe number of columns of a row of coding tree units currently decoded islarger than two, the three memories are activated to transition to theoperating status S0 from the dummy status.

In the operating status S0, there are three conditions as follows.

Condition one: if a coding tree unit currently decoded is the lastcoding tree unit of the current image, then it transitions to the endstatus when decoding of the current coding tree unit is ended.

Condition two: when a first coding tree unit in a row next to the codingtree unit currently decoded starts to be decoded, if the context data ofa coding tree unit at the top right corner of the first coding tree unitin the next row is available (i.e., the context data of a coding treeunit needed for reference by the first coding tree unit in the next rowcan be used as the reference context data), then it transitions to theoperating status S1.

Condition three: when the first coding tree unit in the row next to thecoding tree unit currently decoded starts to be decoded, if the contextdata of the coding tree unit at the top right corner of the first codingtree unit in the next row is unavailable (i.e., the context data of thecoding tree unit needed for reference by the first coding tree unit inthe next row cannot be used as the reference context data), then theoperating status S0 remains unchanged (i.e., the original update memorycontinues to be used for storing the context data of the coding treeunit currently decoded).

In the operating status S1, there are three conditions as follows.

Condition one: if a coding tree unit currently decoded is the lastcoding tree unit of the current image, then it transitions to the endstatus when decoding of the current coding tree unit is ended.

Condition two: when a new slice starts to be decoded or a first codingtree unit in a next row starts to be decoded, if the context data of acoding tree unit at the top right corner of the coding tree unit in thenext row is unavailable, then it transitions to the operating status S0.

Condition three: when the first coding tree unit in the next row startsto be parsed, if the context data of the coding tree unit at the topright corner of the coding tree unit in the next row is available, thenit transitions to the operating status S2.

In the operating status S2, there are three conditions as follows.

Condition one: if a coding tree unit currently decoded is the lastcoding tree unit of the current image, then it transitions to the endstatus when decoding of the current coding tree unit is ended.

Condition two: when a new slice starts to be decoded or a first codingtree unit in a next row starts to be decoded, if the context data of acoding tree unit at the top right corner of the coding tree unit in thenext row is unavailable, then it transitions to the operating status S0.

Condition three: when the first coding tree unit in the next row startsto be parsed, if the context data of the coding tree unit at the topright corner of the coding tree unit in the next row is available, thenit transitions to the operating status S1.

In the end status, it lasts for one clock cycle. Then, it transitions tothe dummy status and the WPP decoding operation is ended.

To ensure that the context data for decoding is already prepared (i.e.,a proper memory is selected for storing data), when a new row of codingtree units starts to be decoded, the memory selection module 28 willoutput a signal to the entropy decoding unit 20 each time switching ofthe operating status is completed.

Hereinbelow, how the memory selection module 28 controls the threememories to store the context data generated in the decoding process inthe three operating statuses will be described with reference to FIG. 5.

In the operating status S0, before a first coding tree unit CTU0 startsto be decoded, storing of the initial context data of the three memoriesM0, M1 and M2 must be completed. At this time, the update memory M0continuously stores the context data of each coding tree unit in thedecoding process, but the buffer memory M1 and the update memory M2 onlystore the context data of the first coding tree unit CTU0 and a secondcoding tree unit CTU1.

In the operating status S1, in the decoding process of a row of codingtree units, the update memory M2 continuously stores the context data ofeach coding tree unit in the decoding process, and the buffer memory M1only stores the context data of the first coding tree unit CTU0 and thesecond coding tree unit CTU1. Moreover, after all the syntax elements inthe second coding tree unit CTU1 are parsed, the context data stored inthe buffer memory M1 is replicated into the update memory M0. When thecontext data in the buffer memory M1 is completely replicated into theupdate memory M0, the memory selection module 28 outputs context datareplication end information to the entropy decoding unit 20, instructsthe syntax element status control module 21 to end the decodingoperation of the current coding tree unit, and gets ready for thedecoding operation of a third coding tree unit CTU2. In the operatingstatus S2, in the decoding process of a row of coding tree units, theupdate memory M0 continuously stores the context data of each codingtree unit in the decoding process, and the buffer memory M1 only storesthe context data of the first coding tree unit CTU0 and the secondcoding tree unit CTU1. Moreover, after all the syntax elements in thesecond coding tree unit CTU1 are parsed, the context data stored in thebuffer memory M1 is replicated into the update memory M2. When thecontext data in the buffer memory M1 is completely replicated into theupdate memory M2, the memory selection module 28 outputs context datareplication end information to the entropy decoding unit 20, instructsthe syntax element status control module 21 to end the decodingoperation of the current coding tree unit, and gets ready for thedecoding operation of the third coding tree unit CTU2. It is emphasizedthat the first coding tree unit CTU0, the second coding tree unit CTU1and the third coding tree unit CTU2 described in each operating statusrefer to multiple continuous coding tree units arranged in the decodingsequence in a row of coding tree units. If it transitions from theoperating status S0 to the operating status S1 and then to the operatingstatus S2, then the first coding tree unit CTU0, the second coding treeunit CTU1 and the third coding tree unit CTU2 described in eachoperating status refer to multiple coding tree units in the current rowof coding tree units decoded in the operating status. For example, thefirst coding tree unit CTU0, the second coding tree unit CTU1 and thethird coding tree unit CTU2 in the operating status S0 refer to multiplecoding tree units in the first row; the first coding tree unit CTU0, thesecond coding tree unit CTU1 and the third coding tree unit CTU2 in theoperating status S1 refer to multiple coding tree units in the secondrow; and the first coding tree unit CTU0, the second coding tree unitCTU1 and the third coding tree unit CTU2 in the operating status S2refer to multiple coding tree units in the third row.

According to an embodiment of the present invention, the buffer memoryM1 functions to cache the context data, and is only responsible forreplicating the context data of the second coding tree unit which hasbeen decoded in the current row of coding tree units into the updatememory M0 or M2. The update memory M0 or M2 is the memory for storingthe context data updated during decoding of each coding tree unit in thecurrent row of coding tree units. Moreover, the two update memories M0and M2 are used alternately so as to ensure that neither of the updatememories M0 and M2 needs to receive the updated context data whilereceiving the context data replicated from the buffer memory M1. Thiscan increase the video decoding efficiency to ensure fluency of thevideo data playing.

In the condition where the number of columns of a row of coding treeunits is smaller than three, the WPP status control module 27 is notactivated. This is because the context data needs to be initializedbefore each coding tree unit starts to be decoded when there is only onecolumn in the row of coding tree units currently decoded, and theinitialized context data during each decoding can be stored by usingonly one update memory. When there are only two columns in the row ofcoding tree units currently decoded, the context data stored in theupdate memory is the context data of the second coding tree unit in theprevious row of coding tree units before decoding of each row of codingtree units. If there is no need to initialize the context data, then thecontext data stored in the current update memory can be directly usedfor decoding of subsequent coding tree units. Therefore, when the numberof columns of a row of coding tree units is smaller than three, theupdated context data can be stored by using only one update memory, forexample using only the update memory M0 or M2.

Of course, the aforesaid embodiment is only a preferred embodiment ofthe present invention, and more changes may further be made in practicalapplications. For example, one operating status may be set for each rowof coding tree units. For a coded image in the WPP mode having multiplerows of coding tree units, five rows of coding tree units are used asthe reference, one operating status is set for each row of coding treeunits, and the buffer static random access memory for caching thecontext data is set and multiplexed reasonably, thereby effectivelyinitializing or replicating the context data during decoding of each rowof coding tree units and achieving true and concurrent WPP CABACdecoding operations.

Finally, it is emphasized that the present invention is not limited tothe above embodiments, and changes such as modifications in the numberof the used update memories, modifications in the number of the setoperating statuses and modifications in true and concurrent WPP CABACdecoding control evolved therefrom should be also included within thescope of the claims of the present invention.

INDUSTRIAL APPLICABILITY

The video decoding device of the present invention stores the datagenerated in the decoding process by using three memories, wherein oneof the memories is a buffer memory and the other two are updatememories. The updated data is written into one of the update memoriesand the buffer memory in the decoding process, and the data in thebuffer memory is replicated into the other of the update memories. Thiscorresponds to that the two update memories receive the updated contextdata and the replicated data respectively, and avoids that the samememory needs to receive both the updated context data and the replicateddata.

The context data generated in the video decoding process of the presentinvention is stored in two update memories and one buffer memory, thetwo update memories are used alternately, and the buffer memory is usedto temporarily store the context data of the coding tree unit acting asthe reference, which is replicated into the other update memory. Thus,the update memory need not receive the replicated data while updatingthe context data.

1. A video data decoding device, comprising: an entropy decoding unit,comprising: a syntax element status control module for receiving anexternal signal and outputting syntax element parsing status andtransition information; a context variable index calculation module forreceiving the information outputted by the syntax element status controlmodule, initializing and updating context data, and calculating indexinformation of the context data; an arithmetic decoding module forparsing original video code stream data into syntax element binary codestring data; and an inverse binarization module for converting thebinary code string data outputted by the arithmetic decoding module intodecimal data; a WPP status control module for selecting an operatingstatus according to a syntax structure of a coding tree unit currentlydecoded; and a memory selection module for controlling the operatingstatus of a memory according to information outputted by the WPP statuscontrol module, wherein the memory at least comprises one buffer memoryand two update memories, and wherein when the number of columns of a rowof coding tree units currently decoded is larger than three, the contextdata of the coding tree units currently decoded is written into thebuffer memory and one of the update memories, and wherein when it isdetermined that the context data of the coding tree units referred by afirst coding tree unit in a next row of coding tree units is availablewhen the next row of coding tree units starts to be parsed, the data inthe buffer memory is replicated into the other of the update memories.2. The video data decoding device of claim 1, wherein: the memoryselection module is further configured to continue to use the originalupdate memory for updating the context data of the coding tree unitswhen it is determined that the context data of the coding tree unitsreferred by a first coding tree unit in a next row of coding tree unitsis unavailable when the next row of coding tree units starts to beparsed.
 3. The video data decoding device of claim 1, wherein: thememory selection module is further configured to, while writing thecontext data of the coding tree units currently decoded into the buffermemory and one of the update memories, write the context data into theother of the update memories.
 4. The video data decoding device of claim3, wherein: the buffer memory and the other update memory only store thecontext data of the second coding tree unit.
 5. The video data decodingdevice of claim 1, wherein: the memory selection module is furtherconfigured to use one of the update memories to store the context dataof the coding tree units currently decoded when the number of columns ofa row of coding tree units currently decoded is smaller than three. 6.The video data decoding device of claim 1, wherein: the WPP statuscontrol module records at least three operating statuses, and the memoryselection module controls switching of the operating statuses of thebuffer memory and the update memories according to the information ofthe operating statuses outputted by the WPP status control module. 7.The video data decoding device of claim 6, wherein: the memory selectionmodule outputs a signal to the entropy decoding unit after controllingswitching of the operating statuses of the buffer memory and the updatememories according to the information outputted by the WPP statuscontrol module.
 8. A video data decoding method, comprising: an entropydecoding step for receiving an external signal and outputting syntaxelement parsing status and transition information, concurrentlyinitializing and updating context data of coding tree units to bedecoded, calculating index information of the context data, parsingoriginal video code stream data into syntax element binary code stringdata, and converting the binary code string data outputted by thearithmetic decoding module into decimal data; and a memory selectionstep in execution of the entropy decoding step, using at least onebuffer memory and two update memories to store the context data, whereinwhen the number of columns of a row of coding tree units currentlydecoded is larger than three, writing the context data of the codingtree units currently decoded into the buffer memory and one of theupdate memories, and when it is determined that the context data of thecoding tree units referred by a first coding tree unit in a next row ofcoding tree units is available when the next row of coding tree unitsstarts to be parsed, replicating the data in the buffer memory into theother of the update memories.
 9. The video data decoding method of claim8, wherein: the original update memory continues to be used for updatingthe context data of the coding tree units when it is determined that thecontext data of the coding tree units referred by a first coding treeunit in the next row of coding tree units is unavailable when the nextrow of coding tree units starts to be parsed.
 10. The video datadecoding method of claim 8, wherein: three operating statuses of thebuffer memory and the update memories are recorded and operations of thebuffer memory and the update memories are controlled according to thethree operating statuses.